TELECOMMUNICATION TRANSMISSION MEDIA In this chapter the characteristics of the media in which the transmission of signals takes place will be discussed. It so happens that we humans basically communicate through speech=hearing and by sight. Human hearing is from 20 Hz to 20 kHz and we can see only the portion of radiation spectrum from about 4:3 Â 1014 Hz (infrared; l ¼ 7 Â 10À7 m) to approximately 7:5 Â 1014 Hz (ultraviolet; l ¼ 4 Â 10À7 m). These communication channels occupy only small portions of the detectable frequency spectrum which has no lower boundary but has an upper. | Telecommunication Circuit Design Second Edition. Patrick D. van der Puije Copyright 2002 John Wiley Sons Inc. ISBNs 0-471-41542-1 Hardback 0-471-22153-8 Electronic 12 TELECOMMUNICATION TRANSMISSION MEDIA INTRODUCTION In this chapter the characteristics of the media in which the transmission of signals takes place will be discussed. It so happens that we humans basically communicate through speech hearing and by sight. Human hearing is from 20 Hz to 20 kHz and we can see only the portion of radiation spectrum from about x 1014Hz infrared l 7 x 10 7 m to approximately x 1014 Hz ultraviolet l 4 x 10 7 m . These communication channels occupy only small portions of the detectable frequency spectrum which has no lower boundary but has an upper boundary of about 1022 Hz gamma rays . Acoustic radiation in the frequency range 20-20 kHz is attenuated quite severely in our environment even when attempts are made to guide it along a conduit. It is therefore quite inefficient to transmit an acoustic signal over any distance which would qualify as telecommunication. The same observation can be made about visible light. To communicate over distances greater than what we can bridge by shouting or see reliably it is necessary to convert the signal into another form that can be guided by wire waveguide or optical fiber or which can be radiated efficiently in free space. Wire coaxial cables waveguides optical fiber and free space transmission have characteristics which vary as frequency changes. A medium may be efficient in one frequency range but quite unsuitable for another frequency range. But efficiency is not the sole criterion for the choice of the frequency to which audio and video signals have to be translated for transmission. To help keep some order and to minimize interference among the various users of communication services it is necessary to assign various frequency bands for specific uses and governments arrogate to themselves the right to demand a .
